DESCRIPTION: There is controversy over the relative contributions of work exposures and personal characteristics in the etiology of carpal tunnel syndrome (CTS), and over effective preventive strategies for CTS. Some have advocated pre-employment screening nerve conduction studies, with the rationale that these studies can predict future risk of developing carpal tunnel syndrome (CTS). Workers at higher risk for CTS can then be kept from jobs requiring intensive hand activity. Though screening for CTS is common, its effectiveness and the role of placement strategies in preventing carpal tunnel syndrome have not been studied. Questions surrounding use of pre-placement nerve conduction studies are part of a larger controversy concerning the relative contributions of different risk factors in the multi-factorial etiology of CTS. We propose a prospective, longitudinal study of 1500 workers who are new or recent hires in a mixture of industries at increased risk for CTS. Baseline data include nerve conduction studies, a medical history, symptoms, physical examination, and job exposures. All workers will be followed for 3 years through repeated questionnaires and collection of administrative data. A sub- cohort of 450 workers, including all those with abnormal baseline nerve conduction studies and matched controls, will receive more detailed followup, including repeat nerve conduction testing and observation of job exposures. Our proposed study will address four aims: Compare the cumulative incidence of CTS in workers with and without baseline abnormalities of median nerve conduction, in order to test the predictive validity of pre-placement nerve conduction studies. Measure the interaction between baseline nerve conduction abnormalities and physical job demands in conferring increased risk of CTS. Measure costs associated with CTS and estimate the costs per case of CTS avoided by pre-placement, post-offer screening with nerve conduction studies. Determine risk factors for CTS in a study that prospectively measures baseline nerve conduction values, job exposures, demographic and anthropometric variables, and history of concurrent medical conditions.